Gold ore cyanide leaching process is the most common gold ore beneficiation process at home and abroad. The technology is mature and the cost is low. However, there are many factors affecting the leaching rate in the cyanidation process, mainly including the concentration of cyanide and oxygen, ore properties, gold particle size, pH value, slime content, pulp concentration, leaching temperature, and leaching time.
The low leaching rate directly affects the progress of the process, so how to improve the cyaniding leaching rate. Today, I will take you to understand what are the factors that cause the low cyanide leaching rate of gold ore?
Gold ore cyanide leaching plants often use sodium cyanide as the cyanide, and the specific amount required depends on the nature of the ore. During cyanide leaching of gold ore, the cyanide content is generally 0.03%-0.08%, and the dissolution rate of gold rises linearly to the peak with the increase of cyanide content, and then rises slowly; when the cyanide content reaches 0.15%, the gold dissolution rate Dissolution rate has nothing to do with cyanide content, or even decreases. In the cyanidation leaching process of gold ore, oxygen or other agents (such as H2O2, CaO2, Na2O2, KMnO4 and Cl2) can be used as oxidants. The concentration increases and increases, and the dissolution of gold is strengthened by oxygen-enriched solution or high-pressure aerated cyanidation.
Some gold ores are not suitable for direct treatment by cyanide leaching. The high content of copper, arsenic, antimony, bismuth and other components in the ore will greatly increase the consumption of cyanide or consume oxygen in the pulp, and reduce the gold leaching rate. If the carbon content in the ore is high, the carbon will absorb the dissolved gold and be lost with the tailings. At this time, pre-oxidation roasting or flotation can be used to eliminate the influence of harmful impurities.
The size of gold particles mainly affects the cyanidation time, and the dissolution rate of coarse-grained gold (>74um) is slow, so gravity separation or flotation is often used to recover coarse-grained gold before cyanidation gold extraction. In addition, it is an important measure to improve the gold leaching rate to fully dissociate the fine gold particles during the grinding process.
In production practice, the pH value of the pulp must be kept between 10.0-11.0. If the alkali content is too large, the pH value exceeds 12 or when the alkali content is too small, the pH value is less than 9, the cyanide leaching rate of gold ore will decrease.
Because the hydrolysis reaction of cyanide will volatilize toxic HCN, lime can be added to weaken the hydrolysis of cyanide and reduce the chemical loss of cyanide, and lime can also neutralize the action of acid substances and precipitate harmful ions in the pulp, making gold The dissolution is under ideal conditions.
Slime content and slurry content directly affect the diffusion rate of components during cyanidation. When there is a lot of slime, the pulp content should be less than 22%-25%, but the content should not be too low, otherwise the consumption of cyanide will be increased.
The diffusion rate of cyanide and oxygen in the pulp will be directly affected by the concentration of the pulp, and too high concentration is not conducive to cyanide leaching. Reasonable pulp concentration should be determined through beneficiation test.
For gold ores with less mud and impurities, high concentration leaching can be used, generally controlled at 40%-50%; for gold ores with complex mineral composition and more mud, low concentration leaching must be used, usually about 25%.
The cyanidation leaching of gold will accelerate with the increase of temperature (caused by the increase of ion activity), but with the increase of temperature, the oxygen dissolved amount will decrease significantly, and the dissolved oxygen amount will be zero at 100°C, making the leaching impossible. conduct. At the same time, the hydrolysis of cyanide itself increases, and the cyanide reaction of base metals accelerates, which increases the consumption of cyanide, reduces the solubility of Ca(OH)2, and causes the pH value of the pulp to be low. Generally, cyanide leaching does not need to be heated, and it can be maintained at 15-30°C.
The cyanide leaching time depends on the nature of the material, the cyanide method and the cyanide conditions. Generally, stirring cyanide leaching is often longer than 24 hours, sometimes as long as more than 40 hours, gold telluride cyanide takes 72 hours, and percolation cyanide leaching takes more than 5 days.
There are no identical mines in the world, and different ore conditions and processing plant conditions, the suitable gold ore cyanidation leaching methods are naturally different, and the technical parameters are also different. It is recommended to carry out the test first, and determine the appropriate cyanide leaching process conditions through the test results, so as to obtain ideal technical and economic indicators.
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